First off im new to bimmerfest and i need help with some questions. please forgive me if this is on the wrong thread.

so i have a 2001 330Ci and im looking into subs. there are a couple options i have been looking at and need some help. im not looking to go crazy and spend a ton of money.

one option would be to get the 6.5" kicker subs and replace the back seat subs. i dont even know if thats possible and if so what kind of difference it would make. and if i did this would i have to get a new amp to go along with the new subs?

another option would be to just get like a loaded box and amp and put it in the trunk.